Electronic apparatus



1942- J. M. HOLLYWOOD 2,306,386

ELECTRONIC APPARATUS Filed April 30, 1941 2 Sheets-Sheet l y 1 Tube 6'INVENTOR ATTORNEYS 2 snts-sheet 2 INVENTOR J. M. HOLLYWOOD ELECTRONICAPPARATUS Filed A ril 30. 1941 h k \NN NW k E hm w jlAAl Dec 29, 1942.

%M ATTORNEYS MAM Patented Eco. 29, 1942 UNITED STATES PATENT OFFICE2,306,386 nmc'momc manarus John M. Hollywood, Red Bank, N. 1., assignorto Columbia Broadcasting System, Inc., New York, N. Y., a corporation ofNew York 18 Claims.

This invention relates broadly to the field of electronic switchingcircuits. The invention particularly contemplates an electronicswitching circuit of the so-called "ring type, but in certain respectsthe invention is of broader application. The invention is particularlyimportant in the field of color television, being especially adapted foruse in changing the balance between difierent color components of acolor television signal. However, the invention may be applied to otherfields of use.

The term electronic switching may be applied to the making of circuitsoperative or inoperative, or the changing from one condition ofoperation to another, by means of an electronic device. The switchingmay be efiected, for example, by a change in polarity or magnitude, orboth, of a voltage or current.

There have heretofore been proposed a. number of electronic switchingcircuits, including those of the ring type, employing gas-filled triodesof the so-called 'I'hyratron" type. The switching is effected byimpressing suitable control pulses on the circuit. In the case of a ringcircuit, the control pulses cause the tubes to be fired successivelyaround the ring. Such circuits, while satisfactory for many purposes,are subject to some eccentricities of operation due to the pres ence ofthe gas. and the abruptness of the switching is limited by the time ofionization and deionization of the gas in the tubes as well as by thecircuit constants required.

A primary object of the present invention is to provide circuitsemploying vacuum tubes, rather than gas-filled tubes, which aretherefore free from the eccentricities of gaseous discharge tubesandfaster in operation. Furthermore, the invention provides circuits inwhich the electronic switching can be readily controlled and involves amin mum of interaction on the control voltagesl In accordance with theinvention, one or more pairs of electronic vacuum tubes are employed,each tube having a plurality of control electrodes. The anode circuit ofeach tube is interconnected with a control electrode of the other tubeof the pair so that anode current exceeding a given value in one tuberestricts anode current in the other tube below a lower limiting value.Preferably the anode current of the tubes is switched betweensubstanially cut-oft and a relatively large value. Control voltages areimpressed on the other control electrodes of the tubes of a pair inorder to switch current flow from one tube to the other. The use of twocontrol electrodes in each tube of a pair facilitates the ready andprecise control of the switching and enables the switching to beperformed'with a minimum of interaction on the control voltages.

For convenience of description hereinafter.

. when anode current is flowing in the second tube of a pair, that pairwill be considered to be in an actuated state, whereas current isflowing in the first tube of a pair, that pair will be considered to bein an unactuated" state. These terms will be understood to be employedfor convenience in description, only, since output voltages or currentsmay be derived from the circuits of either or both tubes of a pair, asthe use dictates.

The ring switching circuit, in accordance with the invention, comprisesthree or more pairs of vacuum tubes interconnected so that current isswitched in the pairs of tubes successively around the ring. Provisionis made whereby switching of current in one pair of tubes to an actuatedstate automatically reswitches the current in the preceding pair to anunactuated state and resets the succeeding pair of tubes so that thenext control pulse can switch current in that suceeding pair to anactuated state.

The specific ring circuit described hereinafter is particularly adaptedfor use in the color mixer described in the application of-Peter C.G'"1d mark, Ser. No. 357,082, filed September 1'7, 1940. In thatapplication a color television signal is passed into three channels andblank ng waves are applied to the channels to blank out all but the redsignal in one channel, all but the green signal in a second channel, andall but the blue signal in the third channel. In order to properlysynchronize and phase the blanking waves with the color televisionsignals, the control pulses for the ring circuit are derived from thetelevision signal. For example, the field synchronizing pulses or thepeaks of the vertical sawtooth waves may be employed.

The invention will be more fully understood by reference to the specificembodiments illustrated in the drawings and the following de scriptionthereof. In the drawings:

Fig. l is a circuit diagram of a pair of vacuum tubes interconnected inaccordance with the invention;

Fig. 2 is a circuit diagram illustrating a ring connection of threepairs of tubes; and Fig; 3 is a diagram showing the manner in which atrain of operating pulses causes current to change in the various tubes.

Referring to Fig. 1, a pair of vacuum tubes A and A are employed havingcathodes K and course be understood that other .types, or tubes, may beemployed i1 desired. The anode'will ordi-:

narily be the plate or the tube, and the control electrodes will be inthe form of grids. Also, the cathodes will usually be thermionic andheated by a suitable current source (not'shown); :The

cathode K or tube A is grounded, and the,cathode K of tube Ais-connected to ground'through if l2. Preferably l2 has a low resistancerelative to that of R. The suppressor grids it andiil are connected tothe respective cathodes, the.

usual manner.

The anode-cathode circuit'of each tube --in eludes an impedance, hereshown as resistance R (8), connected between the-respective anode andthe anode voltage (3+) supply. The anodecathode circuit is completed inthe usual manner by connecting the negative side of the B+.-supply toground. The anode voltage may bebbtained in any convenient manner, suchas fromv bat-s teries or the more usual rectifier supply. Bee tween theanode-cathode circuit'oteach tube and a first control electrode oi'=:theother tube is an interconnection II- II). This interconnection isconnected to the anode-cathode circult at a point of the anode impedancewhich is remote from the cathode so that the a voltage drop through atleast a portion or the impedance is impressed on the control electrodeot'the other tube when anode current flows through theimpedance. Asspecifically illustratedyeach'interconnection is directly from; theanode '0! one tube to the control grid SG of the other tube,

and includes a source of biasing voltage D (D) for biasing each controlelectrode below the potential or the corresponding anode of the othertube. Y

Wih the interconnections asshown, it-willbe seen that when no anodecurrent-is flowing in one tube, say, tube A, there will be nosubstantial voltage drop across resistance R and the algebraic sum of.the anode voltage source B and the additional biasing source D will beim pressed upon the 'grid -SG' 0! tube A. If the voltage of D is smallcompared with that of B, for example, 45 volts against 150 volts, thepotential oi the grid SG' will be highly positive with respect to thecathode K and will exert little if any l m ting action on the flow orcurrent in tube A. when current flows in tube A, howeveruthe an outputimpedance, here shown as a resistance above cut-oi! to allow therequired amount of anode current to flow to produce the desired voltagedrop in resistance R.

It will be understood that the particular tubes. voltages, values ofresistanee, 'etc., given above are .1or,speciile,example only, and theinvention is:,not limited thereto." The selection of tubes. voltages andcircuit constants may vary widely depending on the use contemplated, andwill be clear to thoseskilled in the art from the description; givenherein BEO Q Y. eachglnterconnection is made to a Yn'oiatfo'rthe'anodefcathode circuit of one tube "suchfthatwlncrease {in anodecurrent decreases the 'potential'impre'ssed on the control electrode oithe ..othertube; :The voltage and polarity oi the additional bias sourceis then selected in view of 'the change in potential and other voltagesbetween control electrode and cathode so that the change/in/potentialdue. to current in one tube operateswtheiother-tube between cut-ofland arelatively; large current.

. Consideringnowthe-switching of current from one tubeto -the other,assume that both grids G and- G: are.- biased considerably above cut-oi!and that tube "A is-passing anode 'current, thus impressing: a-potentialon central grid 8G to prevent current flow in tube A. It, now, anegative pulse is applied to grid G of sufficient magnitudetorsubstantially cut of! anode current intube A,.'the. vpltage'dropginresistance R will become verywsmallzandthe potential of grid SG of tubeA willbechanged trom=beyond cut-oi! to a relativelylarge positive value,since the 13+ voltage exceeds that of 1). Current will thereupon flow intube A. It grid G is sumciently above cutofl, sufllcient' anode currentwill flow in tube A to cause the voltage drop in resistance R to biasthe :control grid 8G of tube A beyond cut-on. That is, anode current: intube A exceeding a limiting .valuewill .biasgrid SG of tube A beyondcut-om: (It will :be understood that the term biasing beyond cuteoff.includes "to". cut-oil, Ordinarily a negative potential somewhat greaterthan that Just suilicient to cut off anode current will 'be employed-toinsure reliability of operation.) ThereafterQeven though the negativepulse beremoved from grid G and the grid returned toits initial valuesabove cut-oil, tube A will be prevented from passing'current by thevoltage on 8G. On the other hand, current will continue to flow in tubeA until ca negative pulse is applied tovgrid'G of suflicient magnitudeto subvoltage drop across resistance R reduces the potential on grid SG.By selecting a suitable value of R, in conjunction with the othercircuit constants. the potential on SG will be altered to completely outof! current in tube A.

For specific example, with the battery voltages just given, 6C6 tubes,and anode resistances R,

.R' of. say, 100,000 ohms, theanode current in tube is such that thevoltage drop across the tube i relatively low, say, 10 or 20 volts,andthe voltage drop across resistance R will be relatively large, say,140 or 130 volts. Thus the bias on 8G will be made negative, say 35, or25 volts negative to the cathode K. Under these conditions when anodecurrent flows in one tube, it completely cuts of! current in the other,tube.

Toobtain this operation the potential of the second control electrode inthe tube passing current, for example, G in tube A, must be sufficientlystantially cut oil current therein, whereupon the voltagedrop in R willbecome very small and the voltage on grid 8G or tube A will rise to alarge positive value. It grid G is sufllciently above cutoil', theanodecurrent in tube A will produce a sufllcient' voltagedrop in R tobias grid 8G in tube Axbeyond cut-om'thus preventing current flow inAeven though'the negative pulse on G is removed.

Although the above operation is that preierred, particularly for :theapplication to color mixing :above referred to, wherein abrupt changesin currentpare desired, the circuit constants'may beselected toproduce achange between two diflerent current values. For example, insteadorchanging the current in each tube between substantially cut-oil. and arelatively men value vsubstantially unaffected by control potentials onthe two grids, the current in the tubes maybe changed between a lowervalue and an upper value. The desired lower value may be obtained byadjustingthe voltages of the B and D batteries and the value of theplate impedonce so that the potential on, say, SG when current isflowing in tube A does not completely cut oil current in tube A butlimits it below a lower limiting value. The maximum current flowing maybe limited by appropriately selecting the voltages and anode impedanceor by applying suitable potentials to other control electrodes in thetubes. In the present specification and claims the term upper limitingvalue of the anode current in either tube means the value which willrestrict anode current in the other tube at a given lower limitingvalue. Normally, current in excess of the upper limiting value in onetube will bias the control electrode of the other tube below the lowerlimiting value.

In the foregoing description of the operation, current is always flowingin one or the other of the tubes of the pair. This type of operation isadvantageous, particularly in connection with the ring circuithereinafter described. However, for other uses it may be desirable atintervals to cut oil or restrict current in both tubes simultaneously.This may be done by impressing suitable voltages simultaneously on bothcontrol grids G and G, or on other control electrodes provided in thetubes. Further uses and adaptations of the circuit of Fig. 1 will beapparent to those sk lled in the art in view of the foregoingdescription.

In Fig. 1 the anode-cathode circuit of tube A contains a load impedancel2 and an output circuit connection i3. From the foregoing explanationit will be understood that the current flowing in. resistance l2 -willchange abruptly between cut off and a relatively high value, or betweenlower and upper limits, in accordance with the control pulsesimpressed-upon grids G and G through input circuit connections l4 and15. Output connections may of course be take from any other desiredportion of the circuit where the shape of the current or voltage wave isthat desired.

It is considered advantageous to connect the cross-connections to thescreen grids of the tubes and apply the external operating pulses to thecontrol grids thereof. However, the grids may be reversed if desired. Itwill beunderstood that in the specification and claims the terms firstand second control electrodes are used for purposes of differentiationonly, and do not refer to the order in which the grids are spaced fromthe cathode.

Fig. 2 illustrates a ring connection of pairs of tubes particularlyadapted to yield the waves shown in Fig. 3, when controlled by a trainof uniformly spaced pulses. Fig. 2 employs three pairs of tubes AA',B-B', C-C'. The tubes of each pair are interconnected in the mannershown in Fig. 1. However, batteries D and D of Fig. l are replaced byrespective combinations of a condenser 2|, 2| and a parallel resistor22,

22'. The values of these resistors and condensers should be selectedwith respect to the screen grid current and the frequency of operationto provide a bias equivalent to batteries D, D, as will be understood bythose in the art. Batteries may of course be employed, particularly witha train of control pulses of low frequency.

The train of operating pulses from the input 23 is appliedsimultaneously to the control grids G of one tube of each pair, calledthe first tube for convenience of description. As specificallyillustrated, the pulses are applied to the grids G of tubes A, B and Cthrough respective condensers 24 and resistances 25. For the specificoperation here contemplated, it is desired that an output voltage begenerated by only one pair of tubes at a time. (See Figs. 36, 3e and39.) Therefore interconnections are provided so that only one pair oftubes is in condition for current to be switched from an unactuated toan actuated state by a control pulse at any given time, and theswitching of current in this pair will cause the reswitch of current inthe previous pair, thereby cutting off the output voltage generated bythe previous pair.

To yield this operation resetting interconnections are provided fromeach pair of tubes to a control electrode of a tube of the followingpair adapted to bias the control grid to an upper level above cutoffwhen the first pair is in an unactuated state, and to a lower levelabove cutoff when the first pair is in an actuated state. The levels areselected with respect to the operating pulses so that a pulse cannot cutofi a tube at the upper level, hence preventing the switching of currentin that pair, but can cut oil current in a tube at the lower level,hence allowing current to be switched in that pair.

As specifically illustrated, the resetting connections 26 includeresistances 21 connected, respectively, between the anode circuits ofthe second tubes of the pairs A, B, C, and the grid resistances 25 ofthe first tubes of the following pairs B, C, A. (Following pairs are thenext pairs around the ring from left to right, tube A being consideredto follow tube 0'.)

The point at which the resetting interconnection is. connected to theanode circuit is selected so that when no current is flowing in theanode circuit of any one of tubes A, B, C, a suflicient positive biasabove cutoff will be applied to the grid G of the following tube toover-balance a negative operating pulse from the input circuit 23 andthus prevent the following tube A, B or C, as the case may be, frombeing cut off by the operating pulse. This thereby prevents thecorresponding paired tubes A, B or C from developing an output voltage.On the other hand, the point of connection to the anode circuit is suchthat when current is flowing in the anode circuit the bias above cutoffon the grid G of the following tube is reduced to a value such that anegative operating pulse can cut oil current in that tube. therebyswitching current to the other paired tube and developing an outputvoltage.

In the specific embodiment of Fig. 2, the resetting interconnections 26are connected directly to the anodes of tubes A, B, C, respectively.Thus when any of tubes A, B, C is not passing current, the high positivevoltage of the B+ supply is impressed on the grid G of the followingtube and is sufficient to far overbalance an operating pulse. On theother hand, when a second tube, say B, is passing current, the voltagedrop in its corresponding anode resistance R will reduce th positivebias on the grid G of the following tube C to a lower value above cutoffthereby resetting tube C- and permitting the next starting pulse to cutoil current therein. The

next pulse will then cause current to flow in C to create an outputpotential at I30.

Condensers 24 associated with the resetting interconnections introduce asmall time lag in resetting, if the input circuit 23 is of low impedancecompared to resistor 21, so that a single operating pulse will notswitch current in each pair of tubes in quick succession. If the inputcircuit is of high impedance, other suitablemeans forintrot'akeiilace'bei'oreth name Inthlsmamiemnlyone o aisinconditiontobeactuated byastarting'pulse,

output voltage.

"Cut-oil interconnections are also provided between each pair of tubesand the preceding pair so that when one pair is "actuated" by anoperatingpulse,currentintheprecedingpairwillbe switched to theunactuated state. To accom plish-this result, thecut-oil-interconnections may be connected between the anode circuit ofthe second tube of a pair and a second control electrode of the secondtube 01' the preceding pair, designed so that current flow in one secondtube cuts oil flow in the preceding second tube. In the speciflcembodiment of Fig. 2, the control grids G'oi' tubes A, B, C' areconnected through resistances ii to the control grids 86 of thefollowing tubes B, C, A, respectiveLv, the grids SG being in turnconnected to the anode circuits oi the paired tubes B, C, A.

Thus, cut-oil interconnection B is connected to the anode circuit 01'tube B through the condenser-resistor biasing source II, 22, and to thegrid G of tube A through resistance 3|. When no current is flowing inthe anode circuit oi tube B the control electrode 8G of tube B will beat an elevated potential and this same potential will-be applied throughresistance 3| to control electrode G of tube A. In this condition. tubeA is allowed to pass current under the control oi its control electrodeSG'. However, when anode current is flowing in tube B, the voltage dropin its plate impedance It not only impresses a negative potential ongrid 80 of tube B but also impresses a negative potential on grid Goftube A. Thus, flow of current in tube B cuts oil cur-'rentintubeA,aswellasintubeB.

To summarize the operation of the speciflc circuit of Fig. 2, assumethat the pair of tubes B, B is in the actuated state (B cut oil and Bpassing current) and that the other pairs are in the unactuated state.Grid 3G in tube B will be at cutofl', and so will grid G of tube Abecause of cutof! interconnection 293. Current in B will also have resetthe succeeding pair of tubes C. C by reducing the potential on grid G oitube C to its tionwillobtainimtilthenextmratingwlle comes along.

ThenextoperatingpuleewillswitchcurrentthepairoihibesLA'bycuttingoflcurrentintubeAandtherebvallowingtullcurrenttoflow in A, thus placing tubes A, Ain the actuated state. Theactuation o!-tub esA,A-willintun ireswitchtubesC,C'totheunactuatedstate,in the manner Just described forthe preceding pulse,andwillreeetthspalroitubesB,B'sothatthenextpmsewillactuateEB."

As a result oi the operation just described, it

.starting pulsesot brie! duration recur at,say 120 1 correspondingcurrents of tubes A, B and C. It

will be noted that when current is flowing in one tube of a pair it iscut oil in the other paired tube. V

In the color television system for changing the relative magnitudes oithe different colors in a video signal, described hereinbefore, theoutput waves from terminals HA. "3', IIC may be connected to the threechannels for blanking out all but the desired color in each channel. Theprecise control of the circuit of Fig. 2 by synchronising pulsescorrelated with the color video signal, and the sharpness oi thegenerated rectangular waves, results in very satisfactory blanking.

Any number of pairs of tubes, more than three,

may be employed in the ring connection of Fig. 2. Output voltages orcurrents may be taken from any convenient point where the shape of thewave is that desired. In particular, instead of taking an output voltagefrom output impedances HA, I23, "C, as shown, waves of s milar shape butopposite polarity, may be taken from lower level above'cutofl. An outputvoltage will appear at I33.

When the next operating pulse comes along it will cut ofl current intube C by reducing the potential on its grid G from the lower levelabove cutoi! to a value beyond cutofl'. This will cause iull current toflow in tube C, thus creating an output voltage at 13C. At the sametime, the flow of current in C will cut oil current in tube B throughcutoi! interconnection 290, thus cutting ofl output voltage in "3.Current in C will also reduce the potential on grid 8G of tube C tobeyond cutoii, thus preventing tube C from passing current after theoperating pulse has passed. In addition, current in tube C will resetthe pair of tubes A, A by reducing the bias on grid G of tube A from theupper to the lower value above cutoff. In the meantime, the cutting offof current in tube B will have changed the potential on grid G of thetube C to its upper value above cutofl' (through reset connection thegrids 8G of tubes A, B and C. Blight inl-' perfections in the waves maydictate which should be employed.

It may be desired in a ring oi 11" pairs of tubes to modulate theoperating pulses so that every 1: pulse is distinguished in some wayfrom the others, and to have the output from a particular pair 01 tubesalways follow one oi these distinctive pulses. This operation may beachieved by having a difl'erent resetting voltage applied to thisparticular pair of tubes, so that the resetting is insuiilcient for anyother pulse to actuate this pair, but sufllcient for one of thedistinctive pulses to actuate this pair,

As a specific example, it may be desired in the arrangement of Fig. 2 tohave every third operat'ng pulse larger than the others, and to have theoutput IIA always follow the larger operating pulses. To yield'thisoperation, the resetting voltage applied through connection." to theassociated pair of tubes A, A can be taken from an intermediate point ofthe resistance R which forms the anode resistance for tube C. If thispoint is properly chosen, when the pair of tubes C, C is actuated, theresetting voltage will be at such a level that only a distinctive pulsewill bias the grid G of tube A beyond cut-oil. and

For some applications it may be desired to use a chain connection ofpairs of tubes, instead of a ring connection. This may be effected byomitting the resetting and cut-ofl interconnection between the first andlast pairs. Also. the cut-oil interconnections between pairs may beomitted if desired.

The modification described in connection with Fig. 1 in which current ineither tube changes between lower and upper limits, rather than betweencut-ofl and a large value, may be employed in a ring circuit of the typeshown in Fig. 2, if desired.

With respect to the specific embodiments described herein, it will beunderstood that the circuit elements included in the cross connectionsbetween the tubes of a pair, in the cut-off interconnections and in theresetting interconnections, and the points between which they areconnected, may be changed in many respects by those skilled in the artwithin the spirit and scope of the invention.

In particular, in the specific embodiment described the resetting andcut-ofi interconnections are connected between the anode-cathode circuitof the second tubes of a pair and the proper control electrodes.However, the interconnections may be made to other suitable points inthe connected pairs of tubes if desired. For example, a cathode resistorfor the first tube and sensitive grid control for the second tube madehe employed for cutoff, with more or less success. Moreover, althoughsymmetrical interconnections in each pair of tubes and similaritybetween pairs of tubes are advantageous, unsymmetrical interconnectionsand dissimilar pairs may be employed if desired.

In other respects, also, it will be understood that the presentinvention is not limited to the mere details of design, construction andarrangement of the elements disclosed, since many modifications may bemade by those skilled in the art without departing from the spirit andscope of the invention.

The invention may be employed with advantage for a number of purposes inaddition to those mentioned hereinbefore. In particular, it is useful inconnection with frequency division where the frequency of the output ofone pair of tubes is a sub-multiple of the incoming operating pulses,and in pulse distributing circuits in general.

I claim:

1. In an electronic switching circuit, the combination which comprises apair of electronic vacuum tubes each having an anode, cathode and aplurality of control electrodes, an anode-cathode circuit for each tube,interconnections between the anode-cathode circuit of each tube and afirst control electrode of the other. tube for restricting anode currentin either tube below a lower limiting value when current in the othertube exceeds an upper limiting value, and circuit connections for eachtube for receiving operating pulses and applying the pulses to a secondcontrol electrode of the respective tube to change the potential thereofbetween a potential suflicient to restrict anode current below saidlower limiting value and a potential suiiicient to allow anode currentexceeding said upper limiting value to flow.

2. In an electronic switching circuit, the combination which comprises apair of electronic vacuum tubes each having an anode, cathode and aplurality of control electrodes, an anode-cathode circuit for each tubeincluding an impedance and a source of anode voltage, interconnectionsbetween a first control electrode of each tube and a point of theanode-cathode circuit or the other tube selected so that increase ofanode current in either tube decreases the potential impressed on thefirst control electrode of the other tube, said interconnections andimpedances being selected so that anode current in either tube exceedingan upper limiting value yields and maintains a potential for the firstcontrol electrode of the other tube sufilcient to restrict anode currenttherein belowa lower limiting value, the bias on the first controlelectrode of either tube when anode current in the other tube is belowsaid lower limiting value being sufiiciently above cut-oi! to allowanode current exceeding said upper limiting value to flow, means forbiasing a second control electrode of each tube to allow anode currentexceeding said upper limiting value to flow therein, and circuitconnections for. each tube for receiving operating pulses and applyingthe pulses to said second control electrode of the respective tube torestrict the anode circuit therein below said lower limiting value.

3. In an electronic switching circuit, the combination which comprises apair of electronic vacuum tubes each having an anode, cathode and aplurality of control electrodes, an anode-cathode circuit for each tube,interconnections between the anode-cathode circuit of each tube and afirst control electrode of the other tube for substantially cutting ofianode current in either tube when anode current in the other tubeexceeds a limiting value, and circuit connections for each tube forreceiving operating pulses and applying the pulses to a second controlelectrode of the respective tube to change the potential thereof betweensubstantially cut-oil and a value suflicient to allow anode currentexceeding said limiting value to flow.

4. In an electronic switching circuit, the combination which comprises apair of electronic vacuum tubes each having an anode, cathode and aplurality of control electrodes, an anode-cathode circuit for each tube,interconnections between the anode-cathode circuit of each tube and afirst control electrode. of the other tube, designed so that anodecurrent exceeding 9. limiting value in either tube yields and maintainsa potential for the control electrode of the other tube sufiicient tosubstantially cut ofi anode current therein, means for biasing the firstcontrol electrode of each tube to allow anode current exceeding saidlimiting value to flow therein when anode current is substantially cutoff in the other tube, and circuit connections for each tube forreceiving operating pulses and utilizing said pulses to change thepotential on a second control electrode in the respective tube betweensubstantially cut-off and a value sufllcient to allow anode currentexceeding said limiting value to fiow.

5. In an electronic switching circuit, the combination which comprises apair of electronic vacuum tubes each having an anode, cathode and aplurality of control electrodes, an anode-cathode circuit for each tubeincluding an impedance and a source of anode voltage, interconnectionsbetween a first control electrode of each tube and a point of theanode-cathode circuit of the other tube selected so that increase ofanode current in either tube decreases the potential :impressedion thefirst control electrode of the other tube,;said interconnections andimpedances. being designed so that anode current-exceeding alimitingvalue in either tube yields and maintains a potential for thefirst control electrode ointhe othertubepsume cient to substantially'cut .oilanode current therein, means for biasing: the first controlelectrode of each tube to allow anode current. exceeding said limitingvalue torfiow thereingwhen anode current is substantially cut oil in theother tube, means for biasing a second control electrode of each tubesufilciently' above cut-oi! to-allow"anode current exceeding'saidlimiting value to now therein, and circuit connectionslior each:tube for receiving operating pulses and applying .the pulses to saidsecond control electrode ofthe ,respective tube to substantiallycutofi'anode current therein. I

6. In an electronic switchingtcircuit, the combination which comprises apair-oi electronic vacuum tubes each having an anode, cathode and aplurality of control electrodes, an anodecathode circuit for each tubeincluding an ima,sos, sss

bination which comprises a pair of electronic vacuum tubesleach havingan anode, cathode and a3 pluralityoi control electrodes, ananode-cathodeclrcuitior eachtube including a source oisubstantiallyconstant anode voltage and a resistanceconnectedinzcircuitbetween the corre flp ndingtnodeandsaid voltagesource, interconnections between a: firstcontrol electrode of each tubeland a point: ot the resistance of the othertube remote from thecorresponding anode voltage source, a source 0!: biasing voltage in eachpedance and a sourceiof; anode voltage, interconnections between a firstcontrol electrode voi. each tube and a pointot the impedancepot theother tube remote from the correspondingcathode, said interconnectionsand'impedances .being designed so that anode current exceeding alimiting value in either tube yields and maintains a potential for thefirst control electrode of the other tube suflicient to substantiallycut oil anode current therein, means for biasing the first controlelectrode or each tube to allow anode current exceeding said limitingvalue to now therein when anode current is substantially cut off in theother tube, means for biasing a second control electrode of each tubesuificiently above cut-oil to allow anode current exceeding saidlimiting value to fiowtherein, and circuit connections for each tube forreceiving negative operating pulses and applying the pulses to saidsecond control electrode or the respective tube to substantially cut oilanode current therein.

'1. In an electronicswitching circuit, the combination which comprises apair of electronic vacuum tubes each having an anode, cathode and aplurality of control electrodes,an anode-cathode circuit for each tubeincluding an impedance anda source or substantially constant anodevoltage in series, interconnections between-a first control electrode ofeach tube and a point or the impedance of the other tube remote from thecorresponding cathode, a' source of biasing voltage in each or saidinterconnections, said sources 01' voltage and impedances being designedso that anode current exceeding 'alimiting valuein either tube yieldsand maintains a potential tor the first control electrode 01' theothertube sufficient to substantially cut oil' anode current therein,the bias on the first control electrode of either tube beingsufliciently above cut-on to allow anode current exceeding said'limitingof said interconnectionsior biasing each first control electrode belowthe potential 01' said remote cpoint of: the respective resistance, saidsources orvoltage and resistances being selected sothat anode currentexceeding a limiting value inieither tube yields: and maintains apotential iorthefirst'control electrode of the other tube sumcient tosubstantially cut oil anode current therein; thev bias onzthe firstcontrol electrode or either tube being-.suiilciently above cut-oil. to

allow anode current exceeding said limiting value tofiow therein whenanode current is substantially cut oil. in the other tube, means forbiasing a'second controlrelectrode' of each tube sufiiciently abovecut-oi! to allow anode current exceeding said-limiting value to fiowtherein, and circuit connections for each tube for receiving negativeoperating pulses and applying the pulses to said second controlelectrode of the respective tube to substantially cut oil anode currenttherein.

9,.An electronic switching circuit which comprises a plurality of pairsof electronic vacuum tubes, each 01' said tubes having an anode, cathodeand a plurality of control electrodes, an anode-cathode circuit for eachtube, interconnections between the anode-cathode circuit of eachpaired'tube and a first control electrode of the other paired tube forrestricting anode current in either tube below a lower limiting valuewhen anode current in the other tube exceeds an upper limiting value,circuit connections for receiving a train of operating pulses andapplying the pulses simultaneously to a secpotential level when anodecurrent exceeding said upper limiting value fiows in the second tubevalue to fiow therein when anode current is substantially cut oil in theother tube, means for biasing a second control electrode of each tubesufilciently above cut-ofi to allow anode current exceeding saidlimiting value to flow therein, and circuit connections for'each tubefor receiving operating pulses and applying the pulsesto said secondcontrol electrode of the respective tube to substantially cut of! anodecurrent therein.

8. In an electronic switching circuit, the com of said other pair, saidpotential levels being correlated with said operating pulses so that apulse restricts anode current below said lower limiting value in'a firsttube biased to said lower potential level but not in a first tube biasedto said upper potential level.

10. An electronic switching circuit which comprises three or more pairsof electronic vacuum tubes forming a ring, each or said tubes having ananode, cathode and a plurality oi control electrodes, an anode-cathodecircuit for each tube, interconnections between the-anode-cathodecircuittoi' each paired tube and a first control electrode oi the otherpaired tube for restricting anode current in either-tube below a lowerlimiting value when anode current in the other tube exceeds an upperlimiting value, circuit connections for receiving a train of operatingpulses and applying the pulses simultaneously to a second controlelectrode 01' a first tube of each pair, means for biasing the secondcontrol electrodes of said first tubes to an upper potential level,re-setting interconnections from each connected pair or tubes to thesecond control electrode of the first tube of the succeeding pair forchanging the bias thereon to a lower potential level when anode currentexceeding said upper limiting value flows in a second tube of a pair,said potential levels being correlated with said operating pulses sothat a pulse restricts anode current below said lower limiting value ina first tube biased to said lower potential level but not in a firsttube biased to said upper potential level, and interconnections fromeach connected pair of tubes to a second control electrode of the secondtube of the preceding pair for restricting anode current therein belowsaid lower limiting value when anode current exceeding said upperlimiting value flows in a second tube of a pair.

11. An electronic switching circuit which comprises three or more pairsof electronic vacuum tubes forming a ring, each of said tubes having ananode, cathode and a plurality of control electrodes, an anode-cathodecircuit for each tube including an impedance and a source of anodevoltage, interconnections between a first control electrode of eachpaired tube and a point of the anode-cathode circuit of the other pairedtube selected so that increase of anode current in either tube decreasesthe potential impressed on the first control electrode of the othertube, said interconnections and impedances being selected so that anodecurrent in either paired tube exceeding an upper limiting value yieldsand maintains a potential. for the first control electrode of the otherpaired tube sumcient to restrict anode current therein below a lowerlimiting value, the bias on the first control electrode of either pairedtube when anode current in the other paired tube is below said lowerlimiting value being sufiiciently above cut-oil to allow anode currentexceeding said upper limiting value to flow, circuit connections forreceiving a train of operating pulses and applying the pulsessimultaneously to a second control electrode of a first tube of eachpair, means for biasing the second control electrodes of said firsttubes to an upper potential level, re-setting interconnections from theanode circuit of the second tube of each pair to the second controlelectrode or the first tube of the succeeding pair for changing the biasthereon to a lower potential level when anode current exceeding saidupper limiting value flows in a second tube of a pair, said potentiallevels being correlated with said operating pulses so that a pulserestricts anode current below said lower limiting value in a first tubebiased to said lower potential level but not in a first tube biased tosaid upper potential level, and interconnections from the anode circuitof the second tube of each pair to a second control electrode of thesecond tube of the preceding pair for restricting anode current thereinbelow said lower limiting value when anode current exceeding said upperlimiting value flows in a second tube of a pair.

12. An electronic switching circuit which comrises a plurality of pairsof electronic vacuum tubes, each of said tubes having an anode, cathodeand a plurality of control electrodes, an anode-cathode circuit for eachtube including an impedance and a source of anode voltage,interconnections between a first control electrode of each paired tubeand a point of the anode-cathode circuit of the other paired tubeselected so that increase of anode current in either tube decreases thepotential impressed on the first control electrode or the other tube,said interconnections and impedances being designed so that anodecurrent exceeding a limiting value in either paired tube yields andmaintainsa potential for the first control electrode or the other pairedtube suflicient to substantially cut off anode current therein, meansfor biasing the first control electrode of each paired tube to allowanode current exceeding said limiting value to flow therein when anodecurrent is substantially cut ofi in the other paired tube, circuitconnections for receiving a train of operating pulses and applying thepulses simultaneously to-a second control electrode of a first tube ofeach pair, means for biasing the second control electrode of a firsttube 0! at least one pair to an upper potential level, and a re-settinginterconnection from the anode circuit of the second tube of anotherpair to the second control electrode of the first tube of said one pairfor changing the bias thereon to a lowerpotential level when anodecurrent exceeding said limiting value flows in the second tube of saidother pair, said potential levels being correlated with said operatingpulses so that a pulse substantially cuts off current in a first tubebiased to said lower potential level but not in a first tube biased tosaid upper potential level.

13. An electronic switching circuit which comprises three or more pairsof electronic vacuum tubes forming a ring, each of said tubes having ananode, cathode and a plurality of control electrodes, an anode-cathodecircuit for each tube, interconnections between the anode-cathodecircuit of each paired tube and a first control electrode of the otherpaired tube for substantially cutting ofi anode current in either tubewhen anode current in the other tube exceeds a limiting value, circuitconnections for receiving a train of operating pulses and applying thepulses simultaneously to a second control electrode of a first tube ofeach pair, means for biasing the second control electrodes of said firsttubes to an upper level above cut-01f, resetting interconnections fromeach connected pair of tubes to the second control electrode of thefirst tube of the succeeding pair to bias the electrode to a lower levelabove cut-ofi when anode current fiows in a second tube of a pair, saidlevels being correlated with said operating pulses so that a pulsesubstantially cuts off current in a first tube biased to said lowerlevel but not in a first tube biased to said upper level, and cut-oilinterconnections from each connected pair of tubes to a second controlelectrode of the second tube or the preceding pair to substantially cutoff anode current therein when anode current flows in a second tube of apair.

14. An electronic switching circuit which comprisesthree or more pairsof electronic vacuum tubes forming a ring, each of said tubes having ananode, cathode and a plurality of control electrodes, an anode-cathodecircuit for each tube, interconnections between the anode-cathodecircuit of each paired tube and a first control electrode of the otherpaired tube designed so that anode current exceeding a limiting value ineither tube yields and maintains a potential for the control electrodeof the other tube suificient to substantially cut off anode currenttherein, the first control electrode of each tube being biased to allowanode current exceeding said limiting value to flow therein when anodecurrent is substantially cut ofl in the other paired tube, circuitconnections for receiving a train of operating pulses and applying thepulses simultaneously to a second control electrode 01' a first tube ofeach pair, means for biasing the second control electrodes of said firsttubes to an upper potential level above cut-oil, re-settinginterconnections from each connected pair 01' tubes to the secondcontrol electrode oi. the first tube oi the succeeding pair to bias theelectrode to a lower potential level above. cut-oil. when anode currentexceeding said limiting value flows in a second tube of a pair, saidpotential levels being correlated with said operating pulses so that apulse substantially cuts oil. current in a first tube biased to saidlower level but not in a first tube biased to saidupperlevel, time delaymeans associated with said re-setting interconnections for delaying achange from upper to lower potential levels, and cut-offinterconnections from each connected pair of tubes toga second controlelectrode of the second tube oi the preceding pair to substantially cutoil! anode current therein when anode current exceeding said limitingvalue fiows in a second tube 01. a pair.

15. An electronic switching circuit which comprises three or more pairsof electronic vacuum tubes forming a ring, each or said tubes having ananode, cathode and a'plurality of control electrodes, an anode-cathodecircuit for each tube including an impedance and a source of anodevoltage, interconnections between a first control electrode oi eachpaired tube and a point of the anode-cathode circuit or the other pairedtubes selected so that increase of anode current in either tubedecreases the potential impressed on the first control electrode oithe'other tube, said interconnections and impedances being designed sothat anode current exceeding a limiting value in either paired tubeyields and maintains a potential for the first control electrode or theother paired tube suificient, to substantially cut oil anode currenttherein, the first control electrode 01 each tube being biased to allowanode current exceeding said limiting value to flow therein when anodecurrent is substantially cut oil in the other paired tube, circuitconnections for receiving a train 01' operating pulses and applying thepulses simultaneously to a second control electrode oi a first tube ofeach pair, means for biasing the second control electrodes of said firsttubes to an'upper potential level above cut-ofi,

re-setting interconnections between .the anode circuit of the secondtube 01' each pair and the second control electrode of the first tube ofthe succeeding pair to bias the electrode to a lower potential levelabove cut-oil. when anode current exceeding said limiting value flows ina second tube oi a pair, said potential levels being correlated withsaid operating pulses so that a pulse substantially cuts off current ina first tube biased to said lower level but not in a first tube biasedto said upper level, and cut-oil interconnections between the anodecircuit of the second tube of each pair and a second control electrodeoi the second tube of the preceding pair for cutting oil anode currenttherein when anode current exceeding said limiting value fiows in asecond tube of a pair.

16. An electronic switching circuit which comprises three or more pairsof electronic vacuum tubes forming a ring, each of said tubes having ananode, cathode and a plurality of control electrodes, an anode-cathodecircuit for each tube inc uding a resistance and a source 01'substantially constant anode voltage in series, interconing cathode, asource of biasing voltage ineach of said interconnections, said sourcesor voltage and resistances being selected so that anode currentexceeding a limiting value in either paired tube yields and maintain; apotential for the first control electrode or the other paired tubesufiicient to substantially cut oil anode current therein, the bias onthe first control electrode or either paired'tube being sufiicientlyabove cutofi! to allow anode current exceeding said limiting value toflow-therein when anode current is substantially cut oi! in the otherpaired tube, circuit connections for receiving a train of operatingpulses and applying the pulses simultaneously to a second controlelectrode oi a first tube of each pair, re-setting interconnections froma point oi the resistance oi 'the second tube or each pair remote fromthecathode thereof to the second control electrode oi the first tube orthe succeeding pair for biasing said electrode to an upper potentiallevel above cut-oi! when anode current is not fiowing in said secondtube and to a lower potential level above cut-oil when anode current isfiowing therein, said potential levels being correlated with saidoperating pulses so that 'a pulse cuts oil currentin 'a firsttube biasedto said lower level but not in a first tube biased to said upper level,time delay means associated with the re-setting interconnections fordelaying a change from upper to lower levels, and cut-oi!interconnections from a point or the resistance or the second tube ofeach pair remote from the cathode thereof to a second control electrodeof the second tube of the preceding pair for biasing said electrodeabove cut-oi! when anode current is not flowing in said resistance andbeyond cutoil when anode current is flowing therein.

v 17, An electronic switching circuit which comprises three or morepairs of electronic vacuum tubes forming a ring, each or said tubeshaving an anode, cathode and a plurality oi control electrodes, ananode-cathode circuit for each tube,-

interconnections between the anode-cathode circuit oi each paired tubeand a first control electrode of the other paired tube for restrictinganode current in either tube below a lower limiting value when anodecurrent in the other tube exceeds an upper limiting value, circuitconnections for receiving a train of operating .pulses and applying thepulses simultaneously to a second control electrode of a first tube ofeach pair, selected operating pulses difi'ering from the remainder,means for biasing the second control electrodes of said first tubes toan upper potential level, re-setting interconnections from eachconnected pair oi tubes to the second control electrode oi the firsttube of the succeeding pair for changing the bias thereon to a lowerpotential level when anode current exceeding said upper limiting valuefiows in a second tube of a pair, said potential levels being correlatedwith said operating pulses so that a pulse restricts anode current belowsaid lower limiting value in a first tube biased to said lower potentiallevel but not in a first tube biased to said upper potential level, there-setting interconnection to the first tube oi one pair difiering fromthe re-setting interconnection to other first tubes' so that only saidselected difierent operating pulses restrict anode current below saidlower limiting 4 value in the first tube or said one pair, andinternections between a first control electrode of each connections fromeach connected pair of tubes to a second control electrode of the secondtube or the preceding pair for restricting anode current therein belowsaid lower limiting value when anode current exceeding said upperlimiting value flows in a second tube of a pair.

18. An electronic switching circuit which comprises three or more pairsof electronic vacuum tubes forming a ring, each of said tubes having ananode, cathode and a plurality of control electrodes, an anode-cathodecircuit for each tube, interconnections between the anode-cathodecircuit of each paired tube and a first control electrode of the otherpaired tube designed so that anode current exceeding a limiting value ineither tube yields and maintains a potential for the control electrodeof the other tube sufiicient to substantially cut oil anode currenttherein, the first control electrode of each tube being biased to allowanode current exceeding said limiting value to flow therein when anodecurrent is substantially cut oil in the other paired tube, circuitconnections for receiving a train of operating pulses and applying thepulses simultaneously to a second control electrode of a first tube ofeach pair, selected operating pulses having a magnitude greater than theremainder, means for biasing the second control electrodes of said firsttubes to an upper potential level above cut-off, re-settinginterconnections between the anode circuit of the second tube of eachpair and the second control electrode of the first tube of thesucceeding pair to bias the electrode to a lower potential level abovecut-oil when anode current exceeding said limiting value flows in asecond tube of a pair, said potential levels being correlated with saidoperating pulses so that a pulse substantially cuts of! current in afirst tube biased to said lower level but not in a first tube biased tosaid upper level, the lower potential level yielded by the re-settinginterconnection to the first tube of one pair exceeding the lower levelof other first tubes so that only an operating pulse of said greatermagnitude substantially cuts ofi current in the first tube of said onepair, time delay means associated with said re-setting interconnectionsfor delaying a change from upper to lower potential levels, and cut-ofl"interconnections from each connected pair of tubes to a second controlelectrode of the second tube of the preceding pair to substantially cutofi anode current therein,when anode current exceeding said limitingvalue flows in a second tube of a pair.

JOHN M. HOLLYWOOD.

